1. Field of the Invention
This invention relates to a vacuum chamber for semiconductor manufacturing and it particularly relates to a sealing mechanism of a load-locking chamber.
2. Description of the Related Art
To reduce the device area of a semiconductor-manufacturing device, in place of a transfer chamber, devices for which a load-locking chamber and a reactor chamber were constructed in three dimensions were introduced. These are devices in which, for example, a plate capable of moving vertically, which is provided inside a wafer transfer chamber, seals the opening of a load-locking chamber or a reactor chamber, which is provided in the upper part of the wafer transfer chamber, and causes a state of no airflow for both chambers.
When replacing a wafer, because the pressure within a load-locking chamber becomes atmospheric pressure and a transfer chamber is under vacuum, a plate is sucked into the transfer chamber under great force due to the pressure difference between them. When processing a wafer with a diameter of 200 mm and if the diameter of the plate is approximately 300 mm, this sucking force is approximately 700 Kg.
Normally, to hold a plate against this sucking force, an electromagnetic brake is used. Because this brake uses friction, it is gradually worn away and periodic maintenance becomes necessary.
For manufacturing a wafer with a diameter of 300 mm, the diameter of a plate must be enlarge to approximately 400 mm, and the sucking force will reach approximately 1300 Kg. To accommodate these changes, an electromagnetic brake will become larger and the frequency of maintenance work will increase.
Additionally, in a multi-chamber load-locking device for which a load-locking chamber is divided into two by the vertical motion of a plate, the plate receives a sucking force in the reverse direction at two upper and lower sealing positions. As a result, the frequency of maintenance work including brake readjustment increases.
Further, a plate needs to move quickly to improve productivity. At the time of sealing, the plate, however, needs to slow down immediately before a sealing position to prevent particle contamination from an O-ring seal. Likewise, when the plate separates from the seal, it should move slowly and the moving speed should increase after the plate separates from the seal completely.
Thus, in a multi-chamber load-locking device, complex operation control such as change in moving speeds, operation of a brake, and maintenance become necessary.
Consequently, an object of this invention is to provide, with simple construction, a maintenance-free multi-chamber load-locking device which is equipped with an automatic motion control mechanism for a plate.
To achieve the above-mentioned object, this invention comprises structures described below. In an embodiment of the present invention, a multi-chamber load-locking device is placed between a loading station which places a wafer cassette which houses semiconductor wafers, and a transfer chamber which conveys the semiconductor wafers. The device""s chamber space is divided into two by the vertical motion of a plate which comprises sealing structures with which the chamber space is selectively divided into two by contacting the plate and a state of no airflow is caused. A cylindrical cam is provided with the same axis as that of the chamber; and a rotary actuator is connected dynamically with the cylindrical cam. Accordingly, the turning moment of the rotary actuator is converted to the vertical thrust of the axis and in that the plate rises and descends.
Preferably, the groove is threaded so that the moving speed decreases immediately before the plate contacts the sealing surface and the plate is locked in a state of rest when it contacts the sealing surface.
In an embodiment, sealing structures are formed by O-rings.
The multi-chamber load-locking device of the present invention can be used with various devices for transferring wafers between zones having different pressures. In an embodiment, the present invention can be applied to a multi-chamber load-locking device for transferring wafers between a first-pressure area and a second-pressure area, said device having an interior divided into (i) an upper chamber and (ii) a lower chamber, both of which are for transferring wafers at the second pressure, and (iii) an intermediate section located between the upper chamber and the lower chamber, which is for loading/unloading wafers at the first pressure, said device comprising a divider plate having an upper side and a lower side, both of which are for temporarily supporting wafers, said plate moving reciprocally between an upper position and a lower position. In the above, when the plate is at the upper position, the plate divides and seals the upper chamber from the intermediate section and the lower chamber, wherein the upper chamber is at the second pressure while the intermediate section and the lower chamber are at the first pressure, whereby wafers at the upper side of the plate are transferred between the first-pressure area and the second-pressure area via the upper chamber, and when the plate is at the lower position, the plate divides and seals the lower chamber from the intermediate section and the upper chamber, wherein the lower chamber is at the second pressure while the intermediate section and the upper chamber are at the first pressure, whereby wafers at the lower side of the plate are transferred between the first-pressure area and the second-pressure area via the lower chamber. In the embodiment of the present invention, the device further comprising: a cylindrical cam structure co-axially connected to said plate, wherein said plate moves between the first position and the second position by rotation of the cylindrical cam structure; and a rotary actuator for rotating the cylindrical cam structure.
In an embodiment, the cam structure comprises a cam cylinder having a cam groove which rotates with the rotary actuator, and a support cylinder having a cam follower which support cylinder is attached to the plate and does not rotate, wherein the cam follower is fitted in the cam groove and moves vertically when the cam groove rotates, said support cylinder being provided inside or outside the cam cylinder.
In the above, the cam groove can have a shape threaded into five sections constituted by (I) an upper horizontal section for locking the plate at the upper position, (II) a lower horizontal section for locking the plate at the lower position, (III) a an intermediate section for moving the plate at a predetermined rate, (IV) an upper transition section for connecting the upper horizontal section and the intermediate section, and (V) a lower transition section for connecting the lower horizontal section and the intermediate section, The moving speed of the plate decreases immediately before sealing the upper chamber and the lower chamber with the plate when the cam follower is in the upper transition section and the lower transition section, respectively; the plate is locked upon sealing the upper chamber and the lower chamber when the cam follower is in the upper horizontal section and the lower horizontal section, respectively; and the plate moves vertically at a rate when the cam follower is in the intermediate section.
Additionally, the device may further comprises a vertical beam provided in parallel to the axis of the cam cylinder, and a sliding support which is affixed to the support cylinder and slides on the beam when the support cylinder moves vertically.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.